With recent rapid progress of technology on ink jet printers, there can be obtained records having image quality equal to or higher than that of the records obtained by general silver halide photographic process. Thus, ink jet recording media are also required to have the texture similar to those which are used for silver halide photographic process. As ink jet recording media meeting the above requirement, there are used those which comprise a substrate such as paper or plastic film and a porous ink absorbing layer provided thereon.
As ink jet recording media having gloss, cast-coated papers disclosed in Non-Patent Documents 1-3 have been used. The Non-Patent Document 2 refers to Patent Documents 1-3 as specific embodiments. However, as pointed out in Non-Patent Document 3 (page 43), recording media prepared by the technologies proposed in the above Patent Documents are below the level of photographic papers used for silver halide photography from the point of feeling. This is because when an ink jet recording medium is produced by the above technologies, it is necessary for obtaining sufficient ink absorption to employ an embodiment causing formation of fine cracks on the surface of the recording medium, which damage the texture of the surface.
For solving the problems, Patent Document 4 proposes to produce an ink jet recording medium by curing the coat with electron rays. However, the electron radiation curing apparatus is generally of large-scale, and maintenance and control thereof are troublesome, and besides high administration is required from the viewpoint of labor safety.
Under the circumstances, Patent Document 5 proposes a method for producing an ink jet recording medium by coating a lower layer comprising a pigment and a binder, then providing an intermediate layer containing boric acid, and coating thereon an upper layer comprising a submicron pigment and a binder such as polyvinyl alcohol to be crosslinked with boric acid. According to this method, less cracks occur on the surface of the upper layer, and there can be obtained gloss feeling of the same level as of photographic papers used for silver halide photography.
However, when an ink jet recording medium is produced by this method, a very thick coating layer must be provided for obtaining sufficient gloss or ink absorption, and, for example, in Examples of Patent Document 5, the coat has a thickness of 35 g/m2 in total of the lower layer and the upper layer. It is economically not preferred to provide a coat of such a large coverage on a substrate, and there are further problems that the coat is apt to peel off (to form dusts), which requires careful handling as compared with recording by silver halide photographic process.
Patent Document 5 further discloses that it is preferred to provide the upper layer while the coating composition for the intermediate layer has a specific moisture content. As a result of detailed investigation in this respect by the inventors, it has been found that when moisture content in the intermediate layer is low, gloss of the surface after casting is insufficient. That is, when an ink jet recording medium is produced by the method proposed in Patent Document 5, degree of drying of the coating composition for the intermediate layer is affected by the factors such as temperature and humidity of production site and slight variation in water absorption of the lower layer, which finally unavoidably affects the gloss feeling of the resulting ink jet recording medium.                Patent Document 1: JP-A-2001-010220        Patent Document 2: JP-A-2001-071635        Patent Document 3: Japanese Patent No. 2938380        Patent Document 4: JP-A-2004-330725        Patent Document 5: JP-A-2003-231342        Non-Patent Document 1: Kunio Nohara, “Ink Jet Gloss Paper According to Casting Method (1)”, Convertech, Vol. 32, No. 11, Page 61        Non-Patent Document 2: Kunio Nohara, “Ink Jet Gloss Paper According to Casting Method (2)”, Convertech, Vol. 32, No. 12, Page 46        Non-Patent Document 3: Kunio Nohara, “Ink Jet Gloss Paper According to Casting Method (3)”, Convertech, Vol. 33, No. 1, Page 43        